I have exactly the same problem as you. Here in the forum are several other people who also have the same issue. I even contacted SanDisk about this, requesting a firmware update as their SanDisk Extreme SSD seems to have had the same issue in the past till they came up with a firmware update for it.
You can see this problem appearing in their firmware release notes:
- Improved compatibility with certain systems where SATA link sometimes negotiated to SATA 2 vs SATA 3.
I personally have the SanDisk Ultra II and a Samsung 850 Pro. My Samsung SSD doesn’t have this problem. However every time i restart my computer my SanDisk Ultra II changes from Sata 3 to Sata 2 mode lowering my write and read performance by half.
I already contacted SanDisks support via E-Mail but i don’t think they are going to help me as their answers seem automated.
I would really appreciate if someone from their techsupport could dig deeper into this problem and tell us what’s going on, otherwise i think we have to return our SSD’s to get our cash back.